1. Field of the Invention
The invention relates to a temperature sensitive fluid type fan coupling apparatus which generally controls a rotation of a fan for cooling an engine in an automotive vehicle so as to always supply an amount of cooling air blast to the engine in correspondence to a traveling state.
2. Description of the Prior Arts
As this kind of conventional fan coupling apparatus, a system of transmitting a drive torque of a drive disc to a sealing device box by an oil supplied to a torque transmission chamber is popular, and as a structure thereof, there has been known, for example, a temperature sensitive fluid type fan coupling apparatus structured such that an inner portion of the sealing device box is separated into the torque transmission chamber and an oil reserving chamber by a partition plate, the drive disc is provided within the torque transmission chamber by a drive operation of the drive portion, the oil in the oil reserving chamber is supplied to the torque transmission chamber from a supply hole formed in the partition plate or a cover, and the oil in the torque transmission chamber is returned to the oil reserving chamber by a circulation passage (refer to Japanese Patent Examined Publication No. 63-21048). In accordance with this kind of fan coupling apparatus, the drive torque of the drive disc is transmitted to the sealing device box by the oil supplied to the torque transmission chamber from the oil reserving chamber, and a cooling fan mounted to the sealing device box is rotated, so that, for example, the engine for the automotive vehicle is cooled. Further, this kind of fan coupling apparatus is structured such as to detect a temperature of an atmosphere by a bimetal and increase an opening degree of the supply hole when the temperature increases, or directly operate a valve member by a solenoid valve or indirectly operate the valve member by an electromagnet, thereby increasing an amount of the oil within the torque transmission chamber by increasing the opening degree of the supply hole, increasing a number of rotation of the sealing device box and rotating the cooling fan at a high speed so as to increase a cooling effect.
However , this kind of fan coupling apparatus has problems mentioned below.
That is, when restarting the engine in a state that a large amount of oil exists within the torque transmission chamber or when rapidly accelerating during a travel, the sealing device box (the cooling fan) in a driven side causes a rapid increase of the rotation only for a short time by a large amount of oil existing within the torque transmission chamber in correspondence to the acceleration of the drive disc in a drive side. This phenomenon is generally called as "an accompanying rotation", generates a fan sound and an inconvenient feeling together with the sound, absorbs an engine output and deteriorates a specific fuel consumption.
As means for solving the "accompanying rotation" phenomenon mentioned above, there have been known, for example, a structure made such as to temporarily introduce an oil flowing out from a supply hole in a partition plate to a side opposite to a diametrical direction and supply to an inner portion of the torque transmission chamber therefrom (refer to Japanese Patent Examined Publication No. 63-21048), a structure in which a sub oil reserving chamber is provided by forming a drive disc in a hollow structure, and a system of driving a fan having a large blowing capacity at a low speed rotation.
However, these means have disadvantages mentioned below.
That is, in the structure structured such as to temporarily introduce the oil flowing out from the supply hole in the partition plate to the side opposite to the diametrical direction and supplying to the inner portion of the torque transmission chamber therefrom, since the oil does not flow into the torque transmission chamber from the oil reserving chamber in the case that the engine stops when the oil hardly exists within the torque transmission chamber and a large amount of oil exists within the oil reserving chamber, the "accompanying rotation" phenomenon is not generated when the engine is restarted. However, it is not effective for preventing the "accompanying rotation" phenomenon at a time of restarting in the case that the engine is stopped in a state that a large amount of oil exists within the torque transmission chamber or at a time of rapidly accelerating during the travel. Further, in the method in which the sub oil reserving chamber is provided, there is a problem that it is indispensable to complicate the structure, so that a cost becomes high, and in addition, and a mounting is limited since a size in an axial direction is excessively required. Still further, in the system of rotating the fan having a great blowing capacity at a low speed, since a fan coupling apparatus having a high radiating performance is required since the cooling fan is enlarged, and it is unavoidable to make the fan coupling apparatus in a large size, a cost increase, an increase of a horse power for driving (a reduction of a specific fuel consumption) and a limitation of a mounting are caused, so that it is not preferable.